Generic components require generic types to be PartialEq

[kirillsemyonkin]

#[derive] is not perfect (funnily enough, I wrote this before I found the Rust blog quotation, where they mention it being "Perfect derive"), and Rust generates impls with that derived trait also present for generic parameters (e.g. derive(Clone) does impl<T: Clone> Clone for ...). This would happen even for instances when the requirement for the generic parameter is not required (e.g. an Rc<T> field means the struct does not actually require Clone on T).

yew-autoprops does #[derive(PartialEq)], which means when generating impls Rust will place such a requirement on the generic parameters as well. This means following example will not be valid:

#[autoprops_component]
pub fn Example<T>(something: Rc<T>) {
    html! {}
}

As it comes up with the following error:

can't compare `T` with `T`
no implementation for `T == T`
- required for `ExampleProps<T>` to implement `PartialEq`
- required by a bound in `Properties`
- consider further restricting type parameter `T`: `, T: std::cmp::PartialEq`

As all props fields are probably expected to be PartialEq (which isn't always the case with derive), I suggest manually implementing PartialEq for the props struct, containing comparisons for all the fields:

impl<T> PartialEq for ExampleProps<T> {
    fn eq(&self, other: &Self) -> bool {
        #pats_modified_1 = self; // adds _1 to each field, you also have to check that no name ends with _1/_2, otherwise add more underscores i guess
        #pats_modified_2 = other; // adds _2 to each field
        #comparisons // prop_1 == prop_2 && another_prop_1 == another_prop_2 && ...
    }
}

For generic parameters that are to be used directly as a type of a prop field, the user will have to declare them as PartialEq, which is the case for both derive and manual impl solutions.

This is a breaking problem (you cannot implement a custom PartialEq, unlike with non-autoprops props), and fixing it would improve experience of using generics by a lot compared to non-autoprops components.

[cecton]

Fixed in my port of yew-autoprops